Haptic interfaces permit a user to experience a sense of touch in a virtual or haptic environment. Such interfaces are finding acceptance in virtual reality games and in performing tasks that are virtually imaged. One area which uses virtual images to help a user perform a task is computer aided surgery.
In computer aided surgery, a haptic interface can be used to provide haptic guidance to a surgeon. For example, as the surgeon moves a surgical instrument in real space, constraints may be imposed on the surgeon through the haptic interface that limit his ability to manipulate the surgical instrument. The constraints may be based, for example, upon a desired relationship between a virtual instrument and a haptic object in virtual space. In operation, the surgeon manipulates the surgical instrument robotically using the haptic interface. Constraint feedback is provided to the surgeon through the haptic interface, which imposes a force on the surgeon sufficient to maintain the desired relationship between the virtual instrument and the haptic object.
For example, the haptic object may be a virtual protective boundary for an anatomic structure. The virtual boundary is registered (or correlated) to the anatomy of a patient, and the virtual instrument is registered (or correlated) to the actual surgical instrument. To enable the surgeon to interact with the virtual environment via the haptic interface, a haptic rendering algorithm is employed. Haptic rendering is the process of computing and applying forces in response to user interactions with virtual objects. Using the haptic rendering algorithm, the haptic interface may be configured so that as the virtual instrument approaches the virtual boundary, the force experienced by the surgeon increases. This increasing force provides a warning to the surgeon that he is near the structure of interest and therefore should proceed with caution in order to prevent unwanted penetration into and damage to the structure (for example preventing a drill bit from entering too deeply into a bone).
The present invention addresses this need for an improved haptic rendering process.